全文获取类型
收费全文 | 5829篇 |
免费 | 347篇 |
国内免费 | 1篇 |
出版年
2022年 | 33篇 |
2021年 | 66篇 |
2019年 | 41篇 |
2018年 | 59篇 |
2017年 | 59篇 |
2016年 | 84篇 |
2015年 | 127篇 |
2014年 | 203篇 |
2013年 | 271篇 |
2012年 | 263篇 |
2011年 | 295篇 |
2010年 | 150篇 |
2009年 | 142篇 |
2008年 | 256篇 |
2007年 | 261篇 |
2006年 | 255篇 |
2005年 | 282篇 |
2004年 | 234篇 |
2003年 | 242篇 |
2002年 | 266篇 |
2001年 | 234篇 |
2000年 | 248篇 |
1999年 | 181篇 |
1998年 | 97篇 |
1997年 | 58篇 |
1996年 | 51篇 |
1995年 | 55篇 |
1994年 | 54篇 |
1993年 | 52篇 |
1992年 | 122篇 |
1991年 | 136篇 |
1990年 | 105篇 |
1989年 | 106篇 |
1988年 | 122篇 |
1987年 | 99篇 |
1986年 | 91篇 |
1985年 | 85篇 |
1984年 | 60篇 |
1983年 | 63篇 |
1982年 | 45篇 |
1980年 | 35篇 |
1979年 | 49篇 |
1978年 | 43篇 |
1977年 | 27篇 |
1976年 | 30篇 |
1975年 | 35篇 |
1974年 | 31篇 |
1973年 | 35篇 |
1971年 | 34篇 |
1970年 | 29篇 |
排序方式: 共有6177条查询结果,搜索用时 15 毫秒
141.
Satoru Kobayashi Hiromitsu Saito Masukichi Okada 《Development, growth & differentiation》1994,36(6):629-632
We report a simplified and reliable method for non-radioactive in situ hybridization to whole Drosophila embryos. In the previous method (Tautz and Pfeifle, 1989) the post-hybridization wash, or the procedure for washing non-hybridized probe away from embryos depends simply on diffusion. We modified the method with application of electrophoresis to the wash. After hybridized with RNA probe, embryos were transferred to a small well where an electric charge was given to drive non-hybridized probe away from the embryos. This procedure enables us to acquire a much higher signal-to-noise ratio than that obtained from a conventional method. Furthermore, this is a time-saving method. We propose a term "electro-wash" for this procedure. 相似文献
142.
Sheldon Milstien Naoki Sakai Bruce J. Brew †Charles Krieger ‡James H. Vickers §Kuniaki Saito §Melvyn P. Heyes 《Journal of neurochemistry》1994,63(3):1178-1180
Abstract: Nitric oxide has been proposed to mediate cytotoxic effects in inflammatory diseases. To investigate the possibility that overproduction of nitric oxide might play a role in the neuropathology of inflammatory and noninflammatory neurological diseases, we compared levels of the markers of nitric oxide, nitrite plus nitrate, in the CSF of controls with those in patients with various neurologic diseases, including Huntington's and Alzheimer's disease, amyotrophic lateral sclerosis, and HIV infection. We found that there were no significant increases in the CSF levels of these nitric oxide metabolites, even in patients infected with HIV or in monkeys infected with poliovirus, both of which have significantly elevated levels of the neurotoxin quinolinic acid and the marker of macrophage activation, neopterin. However, CSF quinolinic acid, neopterin, and nitrite/nitrate levels were significantly increased in a small group of patients with bacterial and viral meningitis. 相似文献
143.
Identification of the duplicated segments in rice chromosomes 1 and 5 by linkage analysis of cDNA markers of known functions 总被引:9,自引:0,他引:9
N. Kishimoto H. Higo K. Abe S. Arai A. Saito K. Higo 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1994,88(6-7):722-726
We mapped two loci for ADP-ribosylation factor homologues (ARF1, ARF2) and two loci for cysteine proteinase inhibitors (oryzacystatin-I and -II: OCI, OCII) by linkage analysis of restriction fragment length polymorphism loci in rice (Oryza sativa L.) genomic DNAs using their cDNAs as probes.Oc-1 andArf-2 were found to be closely located to each other on chromosome 1, whileOc-2 andArf-1,both found on chromosome 5, were also located close to each other. The map distances are about 2 cM in both pairs. In each chromosome, theArf locus was located about 27 cM from that of the aldolase gene (Ald-2 in chromosome 1 andAld-1 in chromosome 5). These three genes are in the same order,Ald-Arf-Oc, but in opposite orientations relative to the distal ends of the linkage group. The presence of two sets of three linked genes on chromosomes 1 and 5 strongly suggests a structural similarity of the blocks of the two chromosomes, which probably reflects duplication of the segment. A recent investigation by other workers has shown that these rice blocks correspond to two regions in maize chromosomes 8 and 6, that have previously been shown to share many duplicated nucleotide sequences. It is therefore very likely that the duplication of the region occurred before the divergence of rice and maize during the evolution of the subfamilies of the grasses (Gramineae). In view of a recently discovered possible structural similarity between the small GTP-binding protein superfamily, which includesArf andras proteins, and the cystatin family, the close linkage ofOc andArf loci found in the present study suggests a possible cluster of genes related to the small GTP-binding proteins. 相似文献
144.
N. Ikeda Y. Saito J. Shimizu A. Ochi J. Mizutani J. Watabe 《Journal of applied microbiology》1994,77(2):185-194
Variations between and within individuals, and correlations between concentrations of bacterial metabolites, including putrefactive products, ammonia and short chain fatty acids (SCFAs), enzyme activities, moisture and pH, as well as bacterial composition, were studied in faecal samples from seven healthy adults over a period of 7 months. Large variations, both between and within individuals, were observed in concentrations of putrefactive products. Although values for ammonia, SCFAs, enzyme activities, moisture and pH were generally variable, significant person-to-person differences were observed.
While ranges of log viable counts of the predominant bacteria such as eubacteria, bifidobacteria and bacteroides in each subject remained between 0·2 and 1·3, those of enterobacteria, streptococci (including enterococci) and lecithinase-negative clostridia varied between 0·4 and 3·0. Levels of bifidobacteria, enterobacteria, streptococci and total aerobic bacteria showed inter-individual variations. Correlations were found among certain of the parameters: moisture correlated negatively with p -cresol ( r = -0·707), pH ( r = -0–671) and β-glucosidase activity (GS) ( r = -0·608), and positively with acetic acid ( r = 0·621), while negative correlations were observed in pH with acetic and butyric acids ( r = -0·690 and -0·623, respectively).
No significant correlations were found between bacterial compositions, and other faecal factors such as pH, moisture, metabolic enzyme activities and concentrations of putrefactive products. 相似文献
While ranges of log viable counts of the predominant bacteria such as eubacteria, bifidobacteria and bacteroides in each subject remained between 0·2 and 1·3, those of enterobacteria, streptococci (including enterococci) and lecithinase-negative clostridia varied between 0·4 and 3·0. Levels of bifidobacteria, enterobacteria, streptococci and total aerobic bacteria showed inter-individual variations. Correlations were found among certain of the parameters: moisture correlated negatively with p -cresol ( r = -0·707), pH ( r = -0–671) and β-glucosidase activity (GS) ( r = -0·608), and positively with acetic acid ( r = 0·621), while negative correlations were observed in pH with acetic and butyric acids ( r = -0·690 and -0·623, respectively).
No significant correlations were found between bacterial compositions, and other faecal factors such as pH, moisture, metabolic enzyme activities and concentrations of putrefactive products. 相似文献
145.
146.
Conversion of the Salmonella phase 1 flagellin gene fliC to the phase 2 gene fljB on the Escherichia coli K-12 chromosome. 总被引:5,自引:2,他引:3 下载免费PDF全文
The Escherichia coli-Salmonella typhimurium-Salmonella abortus-equi hybrid strain EJ1420 has the two Salmonella flagellin genes fliC (antigenic determinant i) and fljB (determinant e,n,x) at the same loci as in the Salmonella strains and constitutively expresses the fliC gene because of mutations in the genes mediating phase variation. Selection for motility in semisolid medium containing anti-i flagellum serum yielded 11 motile mutants, which had the active fliC(e,n,x) and silent fljB(e,n,x) genes. Genetic analysis and Southern hybridization indicated that they had mutations only in the fliC gene, not in the fljB gene or the control elements for phase variation. Nucleotide sequence analysis of the fliC(e,n,x) genes from four representative mutants showed that the minimum 38% (565 bp) and maximum 68% (1,013 bp) sequences of the fliC(i) gene are replaced with the corresponding sequences of the fljB(e,n,x) gene. One of the conversion endpoints between the two genes lies somewhere in the 204-bp homologous sequence in the 5' constant region, and the other lies in the short homologous sequence of 6, 8, or 38 bp in the 3' constant region. The conversions include the whole central variable region of the fljB gene, resulting in fliC(e,n,x) genes with the same number of nucleotides (1,503 bp) as the fljB gene. We discuss the mechanisms for gene conversion between the two genes and also some intriguing aspects of flagellar antigenic specificities in various Salmonella serovars from the viewpoint of gene conversion. 相似文献
147.
Soji Kasayama Hiroshi Saito Haruhiko Kouhara Satoru Sumitani Bunzo Sato 《Journal of cellular physiology》1993,154(2):254-261
The androgen-dependent clonal cell line SC-3, derived from Shionogi carcinoma 115, secretes a fibroblast growth factor (FGF)-autocrine growth factor in response to androgen, which is able to bind to FGF receptors. In SC-3 cells, FGF receptor expression is upregulated by the SC-3-derived growth factor, providing a means of amplifying an autocrine loop of cell growth. In the present investigations, the effect of the polysulfonated naphthylurea suramin on this autocrine loop and its amplification in SC-3 cells were studied. Suramin inhibited androgen-dependent growth of SC-3 cells in a concentration-dependent fashion: ~50% inhibition was observed at 25 μM. [3H]Thymidine incorporation into the cells stimulated with partially purified SC-3-derived growth factor was inhibited by suramin in a similar way. Additionally, suramin inhibited acidic (a) or basic (b) FGF-induced cell proliferation, though relatively high concentrations were necessary to achieve the maximal inhibition. Pretreatment of SC-3 cells with suramin decreased cell surface 125I-bFGF binding without altering dissociation constant (Kd) of the binding sites. When the cells were incubated with 250 μM suramin for 24 h, the maximum binding (Bmax) decreased to almost 50% of the control. Treatment with suramin also decreased the levels of FGF receptor-1 mRNA to a similar extent, whereas it appeared not to affect the levels of β-actin mRNA. Moreover, suramin completely blocked androgen- or bFGF-induced accumulation of FGF receptor-1 mRNA. The inhibitory effects of suramin on FGF receptor expression were reversed by simultaneous addition of high concentrations of bFGF. These results indicate that suramin exerts its potent antiproliferative action on SC-3 cells through inhibition of an androgen-inducible autocrine loop involving SC-3-derived growth factor and FGF receptor. © 1993 Wiley-Liss, Inc. 相似文献
148.
149.
150.
Y. Yasuda K. Kanda S. Nishioka Y. Tanimoto C. Kato A. Saito S. Fukuchi Y. Nakanishi K. Tochikubo 《Amino acids》1993,4(1-2):89-99
Summary Germination ofBacillus subtilis spores was initiated by L-Ala and competitively inhibited by D-Ala, suggesting the presence of an alanine receptor. The spores showed alanine racemase activity in the spore coat. To investigate the role of alanine racemase (L D) on germination, net racemase activity was determined using diphenylamine as a germination inhibitor and germination was measured using D-penicillamine as a racemase inhibitor. Apparent affinity of L-Ala to the germinant receptor was more than 1000 times higher than that to the racemase. Germination increased in the presence of D-penicillamine, when the concentration of L-Ala was low and that of spores was high. Racemase activity was optimal at 65°C at pH 9.0 and germination at 43°C at pH 7.2. Under unfavorable growth conditions such as high population of spores in limited nutrients, high temperature and high pH, spore alanine racemase converted the germinant actively to the inhibitor and this conversion may regulate germination for survival of the population. 相似文献